Liquid conductivity measurement systems are used for measuring the conductivity of water and aqueous or non-aqueous solutions in environmental, medical, industrial, and other applications where an indication of the ionic content of the liquid is required.
Liquid conductivity is measured in a variety of contexts to provide a parameter that can be related to bulk ionic concentration. In situations where a single type of ion is present, the conductivity can actually be related to the specific ionic concentration. Even in situations where a number of different ionic compounds are present, the measurement of bulk liquid conductivity can still provide very useful information. Accordingly, there has been widespread adoption and utilization of conductivity measurement by the industry for a variety of different purposes.
Typically, contact-based conductivity measurement systems include a conductivity cell and an associated conductivity meter. FIG. 1 illustrates such a system. A conductivity meter generates an AC voltage that is applied to the electrodes of the conductivity cell. The meter then senses the resultant current flow between the electrodes of the cell. This current is generally a function of the conductivity of the liquid to which the cell is exposed.
The amount of current that flows between the electrodes depends not only the solution conductivity, but also on the length, surface area, and geometry of the sensor electrodes. The probe constant (also called sensor constant or cell constant) is a measure of the current response of a sensor to a conductive solution, due to the sensor's dimensions and geometry.
Contact-type conductivity sensors are generally made from at least two pairs of metallic electrodes spaced apart in an insulating sensor body. The distance between and surface area of the electrodes are defined. During operation, the electrodes are in direct contact with the sample solution. The conductivity of the sample solution can be measured by using either a two-electrode or a four-electrode method.
Conventional manufacturing methods rely on metal in the form of thin/thick film, or a rod as the electrode, and plastic, or ceramic/glass, as the sensor body materials. Issues have risen with conventional manufacturing methods including cost and leakage between the seal and sensor body materials.
Providing a contact-type conductivity sensor that is not only lower cost than previous contacting-type conductivity sensors, but more resistant to leaks that would represent a significant advance for contact-type conductivity sensors.